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    <!-- 【案例】统计数组中元素出现的次数
[1,2,3,1,1,1,2,2,3,3,4]
1出现的次数 4
2出现的次数 3
3出现的次数 3
4出现的次数 1 -->
    <script>
        var arr = [1, 2, 3, 1, 1, 1, 2, 2, 3, 3, 4]
        var res = arr.reduce(function(pre, cur) {
            if (cur in pre) {
                pre[cur] += 1
            } else {
                pre[cur] = 1
            }
            return pre
        }, {})
        for (var key in res) {
            console.log(key + '出现的次数' + res[key]);
        }
    </script>
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